1. Field of the Invention
The present invention relates to a hydrodynamic bearing device which relatively and rotatably supports a load with lubricant interposed between a sleeve and a shaft. The shaft is coaxially disposed with the same sleeve, and has a minimal clearance with the sleeve. More particularly, the invention relates to a hydrodynamic bearing device for securely preventing internal lubricant disposed between the sleeve and the shaft from flowing out of the bearing unit. The invention also prevents foreign matter from infiltrating into the bearing unit.
2. Description of the Prior Art
Normally, any of those conventional bearings provided for fast-rotating component parts of electric equipment or electronic office apparatuses uses a hydrodynamic bearing (a slide bearing) which causes a sleeve and a shaft to rotate relative to each other in order to generate dynamic pressure through the pumping of lubricant interposed between the sleeve and the shaft. Conventionally, there are a variety of sealing means for a hydrodynamic bearing device such as the one using magnetic fluid or the one shown in FIG. 5. The sealing means shown in FIG. 5 has a pair of grooves 52a and 52b in a sleeve 52 (or grooves may be formed on the part of a shaft 51) in order to form labyrinth between the sleeve 52 and the shaft 51. Another sealing means shown in FIG. 6 has a pair of projections 62a and 62b on the sleeve 62 that engage with corresponding grooves 61a and 61b formed on the shaft 61 to also form a labyrinth. As is described in the Japanese Patent Application Laid-Open Publication No. HEI-1-224517 of 1989, another type of sealing means has a secondary land across groove having a predetermined width outside of axial direction of a herringbone-type hydrodynamic groove formed between the sleeve and the groove thereof.
As described above, a variety of techniques have been devised to prevent lubricant between the sleeve and the shaft of a hydrodynamic bearing device from leaking out or foreign matter from infiltrating into the bearing. However, a sealing effect cannot fully be achieved in conventional labyrinth-incorporating hydrodynamic bearing devices such as that shown in FIG. 5. Further, such conventional seal that use magnetic fluid incur cost disadvantage. On the other hand, the labyrinth-incorporating hydrodynamic bearing device shown in FIG. 6 involves the use of a relatively complex structure. In many cases, conventional hydrodynamic bearing devices operate vertically erected. However, such conventional hydrodynamic bearing devices cannot always maintain their vertical posture. Instead, they progressively decline during use gradually changing their positions. Once the devices are declined, lubricant stored in the bearing unit is apt to leak of the bearing shaft, bearing, thus causing critical problems.